Chimaeras - blends created by adding human stem cells to animal embryos - are a growing area of research. Currently, researchers use them to study early embryonic development and create animal models of human diseases. But one major future goal is to engineer animals to grow human organs. They could later be harvested from the adult animal and used for transplantation into a patient. Since September 2015, researchers funded by the US National Institutes of Health (NIH) have been banned from adding human stem cells to animal embryos, creating chimaeras. But a proposal by the NIH released 4 August would lift the funding moratorium, except for certain situations. It would also set up a panel to review the ethics and oversight of grant applications. The new rules shorten the developmental window during which human cells can be introduced into non-human primate embryos, disallowing it before development of the central nervous system. This is intended to limit the number of human cells that would make up the chimaera’s brain. They also prohibit breeding animals with human cells, so as to prevent a human-like embryo from growing in a non-human womb, or the birth of an animal that is more humanized than its parents. Reactions from researchers have been mixed. http://www.nature.com/news/us-agency-lifts-ban-on-funding-human-animal-hybrids-1.20379
